This application relates to a rotor for an induction motor wherein counter-bored holes are formed within the laminated core to reduce the likelihood of tears (cracks) forming during casting.
Induction motors are known, and typically include a squirrel cage assembly as part of a rotor. A stator surrounds the rotor, and the rotor is typically associated with a shaft which is to be driven to perform some use.
The rotor is formed of a pack of central iron laminations which are assembled together. End laminations are assembled at each end of the pack of central laminations. The combined laminations are placed into a mold, and a molten metal, typically copper or aluminum is moved into the mold. The laminations are all formed with teeth and gaps circumferentially spaced between the teeth. The gaps between teeth form slots. The molten metal moves into the gaps between the teeth (i.e. slots), forming bars. The molten metal also flows into cylindrical volumes at each end of the rotor, formed by cavities within the mold. These form the end-rings of the rotor. The bars and end-rings are to be homogeneous as formed by the casting process.
As the metal cools, the stresses across the entire rotor vary due to localized cooling differences. The mechanical joints between the bars and the end-rings have sometimes been subject to tears due to these stresses.